1. Field of the Invention
The present invention relates to a plant sensor capable of determining the growing condition of plants or the like as a growing condition measurement target, by obtaining the reflection rates of measuring light by the plants or the like irradiated with the measuring light.
2. Description of the Related Art
For the purpose of improving the production capacities of agricultural products, it has been considered important recently to accurately know the growing condition of a crop and to produce the crop efficiently. To this end, it is a common practice to irradiate a measurement target whose growing condition is to be measured, e.g., a crop, with two measuring light fluxes having wavelengths different from each other; acquire the light fluxes reflected from the crop; obtain the reflection rates at which the crop reflects the two measuring light fluxes, respectively; and obtain the normalized difference vegetation index (NDVI) that is indicative of the growing condition of the crop, on the basis of the two reflection rates. In order to determine the growing condition of the crop more properly by obtaining the normalized difference vegetation index (NDVI) more accurately; a plant sensor has been proposed which is capable of more properly acquiring reflected light fluxes from the crop (for example, see Japanese Patent Application Publication No. 2010-54436).
This conventional plant sensor is configured to: irradiate a first irradiation area of a measurement target with a first measuring light flux and irradiate a second irradiation area of the measurement target with a second measuring light flux acquire the reflected light fluxes of the first measuring light flux and the second measuring light flux from the measurement target; and determine the growing condition of the measurement target by using these reflection rates of the reflected light fluxes. This plant sensor can more properly acquire the reflected light fluxes of the two measuring light fluxes from the crop by reducing the influence of light components attributed to ambient light, and thereby can calculate the normalized difference vegetation index (NDVI) more accurately. Thus, this plant sensor is capable of more appropriately determining the growing condition of the crop.
When irradiating a growing condition measurement target with the first measuring light and the second measuring light having the different wavelengths, the conventional plant sensor, however, has difficulty in locating the first irradiation area with the first measuring light and the second irradiation area with the second measuring light in exactly the same place, because the plant sensor includes a first light emitter and a second light emitter arranged in a line. More specifically, even though the first irradiation area and the second irradiation area are adjusted to exactly the same place on a plane at a certain distance from the plant sensor, the first irradiation area and the second irradiation area are displaced from each other on a plane at a distance other than the certain distance, because the first light emitter and the second light emitter emit light from positions different from each other. This displacement does not particularly cause a problem when the growing condition measurement target has evenness. However, when the growing condition measurement target has unevenness such as spots or the like, the displacement may act as an unstable factor for receiving the reflected light, and thereby hinder the reflected light from being acquired properly. In this regard, the conventional plant sensor still has room for improvement with the view to more accurately determining the growing condition of a crop.